As mobile device technology continues to develop and demand therefor continues to increase, demand for secondary batteries as energy sources is rapidly increasing. Among these secondary batteries, lithium secondary batteries which have high energy density and voltage and exhibit long lifespan and low self-discharge rate are commercially available and widely used.
In general, lithium secondary batteries use metal oxides such as LiCoO2 as positive electrode active materials, and carbon-based materials as negative electrode active materials. In addition, a polyolefin-based porous separator is disposed between a negative electrode and a positive electrode and impregnated with a non-aqueous electrolyte including a lithium salt such as LiPF6, thereby manufacturing a lithium secondary battery.
During charging, lithium ions of a positive electrode active material are released and inserted into a carbon layer of a negative electrode. During discharge, lithium ions of a carbon layer are released and inserted into a positive electrode active material. A non-aqueous electrolyte functions as a medium that migrates lithium ions between a negative electrode and a positive electrode.
However, the electrolyte is continuously consumed by side reaction in a negative electrode and oxidation in a positive electrode during operation of a secondary battery. Accordingly, when the amount of the electrolyte is excessively decreased, desired battery performance cannot be exhibited and lifespan of a secondary battery is rapidly reduced.
Further, when a large amount of electrolyte is added during secondary battery manufacture in order to resolve the problems, an interface between an electrode assembly breaks, and thus, lifespan characteristics are deteriorated.
Therefore, there is an urgent need for technology to resolve such problems.